Final answer:
The correct completion of the passage identifies the volcanic explosion hypothesis as accounting for the presence of a buried crater, iridium, and shattered quartz.
Step-by-step explanation:
Positing an enormous volcanic explosion at the end of the Permian period would explain the presence of a buried crater, account for the presence of the element iridium (originating deep within the earth), and the presence of quartz having been shattered by high-impact shock waves.
The rationale for this sentence is rooted in the scientific understanding of the events at the end of the Permian period and their comparison with what is known about the end of the Cretaceous period. Significant geological activity, such as a massive asteroid impact and vast volcanic eruptions, can cause the deposition of rare elements like iridium and the formation of unique geological structures, such as high-impact shock wave shattered quartz. In 1980, the discovery of a remarkable spike in iridium levels at the K-Pg boundary alongside a buried impact crater in the Yucatán Peninsula substantiated the asteroid impact hypothesis as a cause for the mass extinction at that time.